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Energy Harvesting

May 27, 2009

I’ve been blogging now for over a year and have covered topics ranging from nano-technology and the future of semiconductors to large scale power generation and transmission. This week marks the 50th anniversary of my company, National Semiconductor. This milestone reminded me of how far we’ve come as a technological race. While writing I’ve often reflected on my past engineering experience to look for examples of how we have improved our way of life. However, in this issue I wanted to take a look forward at one of our civilization’s next big hurdles... our future energy supply.

We are reaching a critical mass where our population will soon exceed 8 billion people - many of whom will be the first generation to use electricity or drive a car. In the midst of our current economic crisis it is hard to imagine global markets surging from the millions of new consumers that will have buying power in the near future due to technology’s reach. As we continue our journey into the 21st century, energy will shape the new economy. It will be driven by the demand for manufacturing, agriculture and transportation. As automobiles begin to shed their gasoline engines for fully electric drives, more electricity will be required to recharge the energy storage onboard these vehicles. A simple shift from burning gasoline to fully electric vehicles will not solve our energy crisis since much of our electricity comes from carbon based fuels such as coal. These shifts will require revolutionary changes to meet the new demands.

As in the beginning of the industrial revolution, there will be change on a scale never before seen. Carbon based fuels have been our energy standard for over 100 years, but are becoming harder to find and reach as well as being responsible for polluting our environment. It is well understood that every day terawatts of power rain down on our planet conveniently provided by our sun. It lights and heats our world as well as drives our weather. However, we currently capture only a tiny fraction of this energy through hydroelectric, wind or solar energy farming.

There are millions of square miles perfect for collecting this free energy, but the technologies are fairly new with some proposed projects reaching incredible scales. For example, in New South Wales, Australia a proposal has been made to build a solar chimney that towers over 3000 feet tall with a heat collector that covers over a square mile. As the air under the collector is heated, it naturally wants to rise due to lower density (like a hot air balloon). As it rushes into the chimney which forms a natural draft, the flowing air will turn huge turbine generators that produce electricity. The energy will then be transferred to the grid and sent to cities where it can be consumed. This is the scale of energy engineering that will become common place by 2060.

Another large scale proposal is to place gigantic solar arrays in deserts around the world. These arrays will either convert solar energy directly into electricity or capture the heat to boil water and turn steam turbines. It has been calculated that a photovoltaic array 100 miles on a side would be capable of providing all of the current energy needs of the United States - and that’s with current conversion efficiencies being under 20% (an incredibly poor efficiency rating).

In practice, placing arrays closer to where the energy is consumed provides great benefit. Combined with "smart grid" technologies, photovoltaic arrays spread over many commercial and residential buildings will be used to gather enough energy to begin reversing the trend of building new large scale carbon based power plants. One of the biggest problems with electrical generation is getting the energy where it needs to be, when it’s needed. The peaks and valleys of electrical demand make power plant operators constantly struggle with keeping the output of the plants balanced with the need. By having local generation spread out over a large population area, peak demands are much easier to manage. It also adds another level of reliability since the local solar generators can form micro-grids allowing them to shed completely from larger grids if necessary without interruption.

Along with solar will be other technologies that can be deployed locally such as wind turbines. Large scale wind farms are a common sight today, but smaller, high efficiency, vertical draft turbine designs will continue to improve and allow almost anyone to harness the wind. As with PV systems, these generation systems will be connected to a smart grid to provide maximum load management.

Many scientists and engineers see an ultimate solution to fusion power in this century. With experiments and even small pilot plants being constructed, the consensus among them is that by 2050 practical fusion plants will be a reality. This is the ultimate replacement for the current infrastructure of carbon fuel or nuclear fission based power plants. But we may find that the fusion reactor we have 93 million miles from earth is all that we need. With PV efficiency improvements and large scale deployment combined with practical storage methods, our technologies may one day be completely driven by the sun.

Think this is far fetched? An average home in the United States consumes around 1000 kilowatt hours per month. Add an electric vehicle, and that may rise to around 1500 kilowatt-hours. So let’s round it up to 2000 kilowatt-hours to completely remove all carbon based fuels such as natural gas and propane. That breaks down to just under 67 kilowatt-hours per day or roughly a continuous 2.8 kilowatt load (roughly the amount of 3 hair dryers running).

Assuming the sun shines 8-10 hours a day, 50% of the days are sunny (even cloudy days produce solar power) and an energy storage efficiency of 50% (laptop batteries are far better than that), a solar PV array would only need to generate around 30 kilowatts while in daylight to meet the entire energy requirement of the home and automobile. Today, even with only 10% efficient PV arrays, 15 kilowatt systems are common and affordable (with tax credits carrying some of the burden). It doesn’t take a large stretch of the imagination to see 30-50 kilowatt systems on every home and business within the next 50 years.

So, while you’re out on a sunny day at the gas station filling up your car and wondering about gasoline futures or wondering what to do to keep your electric bill low enough so you can afford to feed your family, take a look up and realize that all the energy you will ever need is falling on the grass in your back yard - something to think about! Till next time...

October 16, 2008

As noted in one of my recent blog posts, "The Quest for Energy Independence" (June 30, 2008), I get a sick feeling every month while opening my power bill which many of you probably share. As most of you experience, the price of electricity has gone through the roof and there’s possibly no end in sight. As fuel costs continue to surge, so does the price of a kilowatt-hour. We are so dependant on electricity, there’s no going back and who would want to... and we continue to blame the power companies for the rising costs and the fact that we are now large consumers of the stuff. Like anything, it was so inexpensive, we used great deals of energy never thinking we’d run out.

In reality, the power company has nothing to do with my consumption - they didn’t knock on my door and say, "hey, like to try some kilowatt-hours man... you’ll really like it!" They are simply the supplier of a required commodity that used to be a lot cheaper than it is today. They are also at the mercy of the raw material suppliers - coal, oil and natural gas prices have all soared recently so they have passed that burden on to us to maintain their profits as any business would do in their position.

Now, when I built my current home, I estimated the cost of all support systems including electricity... I even added an inflation rate which nicely aligned with my estimated cost of living increases as I looked into my crystal ball to predict the future. When a monthly expense is only U.S. $10 and it doubles, triples or quadruples it might make you angry, but it will rarely stop you from drastically changing your lifestyle. However, when that expense in 2001 was US$190 and 7 years later the same expense is US$700+, it drastically affects you’re the way you live and the way you view the future.

If I would have known that the cost of electrical power would rise to such extents in such as short timeframe, I would have made different choices during construction of our home. For example, the house would have been constructed like a thermos bottle (at a much larger expense - initially). HVAC equipment (heat pumps) accounts for the largest consumption of power only second to refrigeration and lighting - especially in hot climates such as Florida.

The cooling systems in our current home had the highest Seasonal Energy Efficiency Ratio (SEER) at the time. This rating is defined as the total British Thermal Units (BTUs) per cooling season divided by the total electrical energy input in watt-hours. Our home required three heat pump units. Two were 2.5 ton units and one was a 1 ton unit. The combined requirement for the house by the contracted design at peak temperatures (in Florida) required 72,000 BTU/hour of cooling!

To keep the house cool, the systems run during peak months for 15 hours per day (1800 hours per season) which results in a power consumption of 10,800 kWh of energy! At U.S. $0.16 per kWh, that is US$1728.00 per season (4 months) or over US$430 a month just to keep the house cool. If you add in lighting, refrigerators and various pumps (e.g. irrigation, etc.) the cost skyrockets! Additionally, high energy users get hit with additional taxes from the power company. They don’t give you a discount for using more... they charge more per kilowatt-hour and the break-point is at the first 1000 kilowatt-hours which we quickly surpass during hot months.

To address the problem you can go back and improve insulation, plant shade trees, apply solar film to your windows, and more. However, somewhere along the line there will be nothing to stop heat transfer - after all, most houses are not designed as Dewar bottles - not yet anyway. So you’ve done your part, but the cost of a kilowatt hour will continue to rise and until electrical energy is as accessible as dirt, there will be no end in sight.

So what can you do to battle the rising costs beyond conservation? How about building your own power plant! That’s right... you and your neighbors. Technology can be a wonderful thing. Today there’s micro wind turbines such as those made by Helix Wind, low cost Solar Photovoltaic panels such as those being pioneered by Nanosolar, and even moderate sized hydroelectric systems designed for large streams (some dam building required) like those from Canyon Industries for those who live in mountainous areas.

I was particularly excited about the small wind systems and imagined a corner of my neighborhood with dozens of these turbines generating power. My thought would be for our Home Owners Association to purchase and install the turbines and sell the power back to the community at (hopefully) a much lower cost than the power company. The other method would be to meter (via the local utility) what goes back into the grid and equally apply credits to all the homeowners! These systems are virtually maintenance free and are designed for a 30 year lifespan. What’s even more interesting is the availability of tax credits or grants for installing alternative energy generation capability!

So if you’ve conserved as much as possible, think about generating your own electricity! If I didn’t have to drill 5 miles to find temperatures high enough to generate super heated steam, I might even consider a backyard geothermal plant, so low cost solar panels will probably be next. Till next time...

October 10, 2008

If you’ve never been to Kansas, you should go - especially the out lying towns that sprung up in the early 1900s to handle the grain produced by the heartland of America. Recently I was on a family vacation to visit relatives and found myself driving for miles and seeing nothing but fields of various grains in every direction. This is the most flat yet beautiful country side I’ve ever seen. Everywhere you look you see various crops and once in a while a lonely group of cows or an abandoned rail line.

While driving the endless expanses of the Kansas planes we would periodically come across a farm house with an outcropping of trees. In every instance I noticed something unusual... all the branches and leaves of the trees pointed in the same direction as if they had been growing toward the horizon. As we drove through little towns such as Chase (which didn’t even have a stop sign) the scene repeated itself - more trees with growth in only one direction... weird.

When we arrived at Great Bend (our first destination) I stepped out of the car and was immediately pushed off my feet by a strong wind - my giant brain suddenly realized why the trees were all growing in the same direction... a never ending breeze across the planes. After we were settled into our hotel I started thinking about all the flat open land we had just driven over and wondered why no one had thought of building wind farms here. After all, crops can easily grow under a large wind turbine - unlike a giant solar array that would screen out the sun light.

The problem occurred to me that this area is somewhat arid and requires irrigation. Most farmers use Center Pivot Irrigation which uses a deep well and a large mobile arm that traverses an arc or complete circle. While it moves it irrigates the crop below and can be easily moved out of the way for harvesting. If you built wind turbine towers in this area you’d have to be strategic on where you locate them.

My initial thought was that they would interfere with the farmer’s ability to use these irrigation machines - but with a little thought I realized you could actually build the turbine towers in the corners of the square property plots and never interfere with the irrigation or harvesting - effectively double farming the land for both crops and energy (see illustration).

The only other problem I could see was the lack of an infrastructure to either store or transport the energy produced. Building the wind farms would be straight forward and probably could be done in very little time following harvest. However, the high tension lines required to move the newly generated power could be a problem - you’d need right-of-ways for those large towers and high power lines...

The other option is to use the power locally, but that would require some form of storage. The weak link of both solar and wind is the current inability to effectively store the energy produced. If you could store it and run machinery on it (e.g. crack water and run farm equipment on the hydrogen produced) you might find people more readily willing to have these large fans sitting on their property. All things considered, I believe there are natural energy resources just waiting to be tapped - this is just another example. till next time...

September 16, 2008

What if you could simply lay your cell phone and Bluetooth headset on a charger plate and charge it up without wires. You may very well be doing just that very soon... Now imagine those chargers are everywhere!

The whole idea of powering something without wires goes as far back as Nikola Tesla circa 1891. His ideas of providing wireless power to equipment located anywhere was a bit "out there", but he had the right idea. He even made comments that someday, "our machinery will be driven by a power obtainable at any point of the universe." That brings to mind thoughts of zero point fluctuations and such. However, I’m diverging... today, my wife has an iPhone and I have a Blackberry - both devices lack a zero-point energy generator, but they do have batteries. Both devices have good run times, but we always need to plug them in at night or risk running low on power during the day. This also includes recharging our Bluetooth ear buds...

A new technology called Vertical Fountain Flux inductive charging is about to change the way we charge our mobile devices. Typical inductive chargers use a high power magnetic flux to pass energy to a device such as a pacemaker (located inside your chest) and charge the batteries. This type of charging is fairly efficient at close proximity, but can also damage hard drives or erase the magnetic strips on credit cards.

A company called Convenient Power has created technology based on VFF techniques which localize the magnetic field so it exists only between the device under charge and the charger (not everywhere). This is highly important for magnetic media or other magnetic sensitive devices that are nearby. It appears that the technology is independent of orientation and is capable of charging 20+ watt devices making it fairly universal for most portable equipment.

Now imagine a solar powered VFF charger platform... when nothing is on the top of the surface, solar cells collect ambient light from the house or office and charge onboard batteries or super-capacitors (or a combination of both). When you return your mobile device for charging, it transfers the energy stored in the platform and charges the device’s batteries. How cool would that be? A charging station that can be located anywhere there is ambient light and can charge your mobile device without plugging it in... I want one!

I can imagine these types of chargers built into places you visit everyday - for example your car. I’d love to simply lay my phone down in the console and have it charge up automatically while I drive to work. Once I arrive I could lay my phone on another charger sitting in my office which was busy charging its own batteries while I was away. I could finally cut the cord that ties me to wall power. And as mentioned on Convenient Power’s website, a formal standard for devices to recognize the chargers and use the power would make charging as universal as cellular networks. No more looking for a compatible charger - they’d be everywhere!

So let’s get rid of that last meter of power cable and have free charging for all... just like Wi-Fi, maybe there’ll be a little sticker on the window of your favorite coffee establishment that reads, "Free Wi-Po"... just a thought. Till next time...

July 29, 2008

What if someone were to tell you that you could build a product that, following manufacturing, would use zero power and produce no carbon emissions? My first response would be, "yes, if you have abundant energy in the product’s environment that could be harvested efficiently". So what "energy" is there to harvest? Let’s take a look at the available sources and methods for creating a zero power system and what limitations exist today that limit the performance.

First, we need to have energy of some sort to power our device. Energy resources will limit the performance of our system, so knowing our energy limits is the first step in determining what is possible. Here’s a list of sources and the availability of each:

TYPE

ENERGY DENSITY

AVAILABLIBILITY

IMPLEMENTATION COST

SOLAR (PV)

HIGH

HIGH

MEDIUM - HIGH

WAVE

HIGH

MEDIUM

HIGH

TIDAL / LUNAR

HIGH

MEDIUM

HIGH

GEOTHERMAL

HIGH

LOW

HIGH

WIND

MEDIUM

MEDIUM

MEDIUM

VIBRATION

LOW

LOW

LOW

THERMAL

LOW

LOW

LOW

PRECIPITATION

LOW

LOW

LOW

RADIO EMISSIONS

LOW

HIGH

LOW

ZPF

?

HIGH

?

OK, The ZPF (Zero Point Fluctuations) line item is a stretch - but I included it since at the nano-scale, it actually may be a source of energy and it does exist. So, out of the above list solar is probably the best for most applications. Depending on the season and where on earth you are located, the sun rains down energy on the surface anywhere from 2 kWhr/m^2 to over 7 kWhr/m^2. For applications such as buried high-way sensors, vibration could be a good source of power (and even solar). Water running down a drain could also be tapped to supply power to small monitoring systems. If the equipment is really frugal with its power, radio emissions from the many radio and TV stations could be harnessed to supply microwatts (possibly charge capacitors for use later).

To understand what it would take, let’s use an example of a system I saw many years ago that really needed to be completely independent from any power source - a golf course sprinkler head. This was a neat idea that a major irrigation manufacturer dreamt up (and you know who you are...). Here was the problem - a golf course must have water to keep "green" and the system must easily adapt to changes in the location of traps and greens. Conventional zoned systems that use wires cannot easily be moved. Each head needs to be controlled and require power. Each head is used a few hours each week.

So the solution was to have each irrigation head be a self contained system that was totally independent and could be installed anywhere along a pipe without requiring any power. Each head would communicate wirelessly to repeaters (or a mesh network) controlled from a central PC. Moisture sensors could also be spread around the network to more accurately control the irrigation so not to waste water. To solve the problem of power, at the top of each head a small solar panel was used to charge a battery (the weak link - batteries require replacement) capable of opening the valve and maintaining the electronics. If the grass started to grow over the solar panel while the head was off or the battery required replacement, the head could signal a problem to the central computer.

The overall function was to water the grass under control from a central system, require no external power source and rarely need service - a very nice application of a completely autonomous system harvesting energy to perform its function. Could it be improved? How about using the high pressure water during the watering cycle to run a small turbine and charge the battery - helps if there’s not enough sun. Of course low power electronics makes this all possible (see http://national.com/powerwise for more information on reducing energy consumption in electronics). If the electronics draw more power than the solar panel can supply (and the head is small), then the battery will go dead (along with the grass). Additionally, the valve must use hydraulic pressure to help hold it open to minimize the energy required - a common feature of irrigation valves.

Let’s take a look at another system - this one hypothetical; an attic temperature sensor. The idea here is to monitor the attic temperature for control of an exhaust fan that helps reduce the cooling cost of the home. Now there’s a new problem - no direct sunlight and limited ambient light. There are several sources of power in the attic, but most notably a large differential temperature (in summer or winter). So the question is, how could this sensor be built? I’m going to suggest a thermal generator charging a battery or capacitor. During times of peak temperature differentials such as mid-day in summer, the generator charges the battery and monitors the temperature communicating wirelessly to the controller in the fan. The actual device could be shaped like a spike that is thrust into the ceiling wall-board and protrudes through the insulation. The cold side is inside the house (in the ceiling) and the hot side is in the attic... could it work? You tell me... till next time!